Ugh, I'd really struggle with that. It seems she should do her best to keep the disruptions out of the time you're paying for.

One positive thing about my ex-T is that she kept her phone in her purse turned off during session.

Ex-MC always had his phone on (and not on silent, so I'd hear very clearly when he got texts, rather than just a buzz) and would sometimes say "I just have to check the number." The worst was a couple times when he said "I have a couple potential emergencies brewing, so I have to check." He worked with high-risk teens (plus, at the time, his wife being sick). Those times were difficult because it felt like any moment, he might get a text and have to end the session. Once, he did take a call from a client, thinking it was an emergency (he stepped out of the room), then came back a minute later saying it was not an emergency.