Totally disagree with this.
She might have cried in just the same way if her daughter had come to her and said she'd lost her virginity to a lad.
It seems more that the crying is an outpouring of emotion about her child growing into an adult, and the concerns she has around that. She doesn't have any issue with her child's sexuality of itself.
If her daughter was straight, she might fear teen pregnancy, physical abuse etc.
With her daughter being gay, she might fear a harder route to pregnancy, homophobic treatment from others etc.
All legitimate fears of a doting mother.
There's also an enormous difference between being homophobic and worrying for someone because of the challenges they may face as a result of being gay. I think to ignore those potential challenges / difficulties is ridiculously ignorant and also pretty offensive to gay people who face those challenges / difficulties.
A conversation I had with my cousin and his husband, some years ago, about travel, has always stuck with me. We were talking about potential holiday plans and he started going through countries they'd like to visit but have to avoid due to their sexuality and the laws in those countries. I love my cousin and his husband dearly and I was simply just incredibly sad for them. It genuinely affected me and I had a bit of a cry about it later on. Not because I'm homophobic and have a problem with them being gay but because I was so upset that their experience of the world is different to mine purely because they love each other, rather than women.
They've recently had to move to a new neighbourhood because, despite being in an affluent blue state, they found their children were being excluded from parties, play dates etc as a direct result of the children's peers' parents being homophobic.