That is not at all how I read it. She was thinking about Val more than anything else.
Nothing’s changed regarding her mother, she could just continue to not tell her. There’s no reason to break up because of that. Juls only brought it up as a reason Val could accept, since “I’m doing it for you” would never fly.
The whole framing, of the previous episodes and this one and this specific conversation, are making it much more about Juls’s issues with her place in Val’s life and the disruption she’s causing to it than anything else.
To put it simply, everyone around her, everyone who has any kind of remotely positive interest in Val or her, has said they won’t last, that she’s bringing trouble to Val. She just had Val’s sister show up and say she’s destroying Val’s life and then found out she couldn’t even get in the car. That. Would. Be. Mortifying. Would she want Val to go through that? For her? Tbh, I don’t think she’s actually correct in making this decision because it’s not up to her to make, it’s Val’s. But she thinks she’s not worth it. That’s the biggest tragedy here and the takeaway. That the people around them have put them in this position.