My gf , Eight years my junior at 24, who wants a monogamous relationship with-out a long term commitment at the moment because of career path, children, her view of the marriage commitment paradigm, and flexibility of lifestyle relocation. among other reasons. I'm rooted in my city and do not want children she is unsure of her view of having children bit knows that she would not want any until her career path has matured.
Her mother (divorced because of her having an affair, mother to an out of wedlock daughter 13 years younger than her youngest child by a father 7 years her junior and at the time sleepover dating another guy a number of years her junior) to my gf, who had shared my house and bed for two years, that if I came to their city for Thanksgiving weekend we could not share a room 'under my roof'.
We laughed rented a hotel room and came for the week-end.
Families are odd be they yours or others.
Old enough to be in a seven year relationship is old enough to put your foot down. I consider her family and she considers you family so get over what ever issues because you will not like the outcome of a me or her position.
Your gf has been with you seven years whether your Mom comes around or not she will always be your mom . Your gf is a free-agent do not lose her to the draft thrown off from your Mothers cold shoulder.