Reading for VenusRising
This is a question relating to the feelings of the mother of your boyfriend. The chart cast has Sagittarius rising, ruled by Jupiter. As the hour ruler is also Jupiter the chart is radical. There are no considerations before judgement.
You are signified by Jupiter, in the third House in Aries. Although Aries is a Fire sign, and Jupiter rules the Fire triplicity by night, the chart was cast just before sunset, so the Sun is still triplicity ruler (the Sun rules by Day). Jupiter does have some dignity through terms, but overall is not very strong.
The next issue is to find the significator of your boyfriend's mother. Two approaches to this are:
Firstly, that of John Frawley who would always use the seventh House for the other person unless they have some clearly stated role which takes them out of the seventh, such as a friend, brother or sister, parent or child. Here the relaionship is boyfriend's mother so the mother is not seventh House. Frawley would say that the boyfriend should be given the seventh, no matter how ephemeral the relationship. This would be the tenth house from the house of the boyfriend (seventh House) bringing us to the fourth House of the radical chart. The fourth House has Aries on the cusp, so it's ruler is Mars. The Seventh House has Gemini on the cusp and so he is signified by Mercury.
The second approach is that of Lee Lehman, who sometimes uses the fifth house for a romantic relationship, the deciding issue being not the length of time of the relationship but the feelings/attitudes of the couple. It's clear that you see this as a committed relationship so again the seventh would seem the appropriate House for your boyfriend, which also brings us to Mars as the significator of his mother.
However if HE thinks of the relationship in a different way, Lee might well use the fifth House for him, which would give us the radical second House as the house of his mother and Saturn as her significator.
Personally I'd go for the Frawley approach rather than Lehman's and as her first take would also use the seventh for the boyfriend I'll use that approach.
Her significator is therefore Mars, in the eighth House in Virgo, which is ruled by Mercury. We could judge her feelings and sympathies from the essential dignities of Mars' placement. Her main feelings are for Mercury, which we have seen is her son, and this seems to fit your description of her. Mercury is also exalted in Virgo, so she really adores him. The triplicity ruler is Venus, the Terms ruler is Mercury (again!) and the Face ruler is the Sun. Mercury rules three of the five essential dignities, so she really does almost worship him. The issue is who is Venus - Venus rules the MC and tenth House - which is the fourth House from the seventh and the opposite House to hers. This is the house of her partner and (usually) his father. If her partner is not his father, then it's her partner that has her affections, assuming she has one, otherwise it's his father.
The Sun rules Leo, intercepted in the eighth house - his house of possessions and income. This is the least important thing for her, and is probably simply a reflection of her wanting the best for him.
Do you (Jupiter) feature anywhere? Well Virgo is the detriment of Jupiter, so her feelings towards you are not positive. Given the strong feelings for her son, I'd guess she might see you as a threat and it's that that she doesn't like, not you as a person. Your task is therefore to show that you are not a threat, and that she's gaining a daughter, not losing a son.
Would there have been a different outcome if I'd used Saturn as her significator, following Lehman's second line of approach? Saturn is in Virgo!! The only difference would be that Saturn is in its own terms, and so she would have some feelings for herself and slightly less for her son (though still pretty overwhelming) and Saturn is in the Face of the Moon, which rules Cancer, the sign on the eighth cusp and his money and resources.
Whichever approach I use, I get virtually the same result. Even if I decide to use the Moon as her signifiator, being an older woman, I find the Moon in Gemini, ruled by Mercury and with Jupiter in detriment.
I think you already suspect that her feelings are hidden and not particularly positive - but I still think it's your role, not you that she doesn't like - any girlfriend would be viewed in the same way.
At the moment there doesn't seem to be any overt hostility, so there's still hope for improvement. Work on her and Good luck!