

“Hey, GF, what did you think of this format? I want you to have fun, but I’m worried that you’re not enjoying it. It also seems like there are some unspoken expectations from the others, and I think it’d be good for us to discuss them together to see if we agree with them, and then maybe take our thoughts to the group.”
And then be ready to either defend your GF, as well as open to potentially leaving the group with her if the other players refuse to accommodate.
Just because you think the right solution is for your GF to increase her pacing does not mean that your GF will agree with the premise, and even if she agrees, it doesn’t mean that she can achieve whatever arbitrary standard the group expects.
Great! Then either talk to her to come up with ideas, or if you’re determined to ask the internet, telegraph your united front in your question so that we don’t assume that the primary reason is that you are a shitty partner. Read your question again, just the words, and see if it sounds like the author actually likes their partner, or wants help from the internet changing them to make this game more fun for themselves?
Anyway.
A live session with just voice chat is already a heavy mental toll for some people. Players and DM alike are filtering and translating ideas through one or more layers (what should be done? would this PC/NPC think to do X? How does doing X look like in this setting? Do they have the materials necessary? Would they countenance doing X based on their personality? What would they say alongside it, with what accent and affect?) in real time. Imagine trying to also type while thinking through those thoughts, and wanting your words to be well written, and your grammar and syntax to be correct, and your immortal words to be self-consistent across multiple posts? AND while you are working on all those things there is also distracting crosstalk? Or worse, you’re in a quiet room typing by yourself, but you know that three or more people are talking about what you’re typing in a little huddle? There is no consistent human response to this situation.
It’s an objectively complex format. Some people may find it easy. Some people may be able to ignore or eschew some of their own internal requirements that are consuming their mental energy and game time. And some people may not, and then external pressure to do so can make them stressed, which makes all of what I wrote harder to manage.
You could go text-only, with multiple text channels (roleplay vs ooc vs initiative) and strict timers, e.g. 5 minutes (which, speaking from personal experience, is also draining) just get rid of the voice chat. Or as others said, go with truly async play-by-post with 24 hour timers. Sure, a single combat may take a week to resolve, but it gives everyone plenty of time to do all of the mental load required to play, without all the pressure of realtime translation.