Help with arm and shoulder position in squat for new client

Hi there,
I have a new female client that Im coaching. She is two sessions in and is constantly complaining about arm and shoulder pain DURING the squat, not after. I can see that she is physically in pain during and after the squat because her arms are hurting so bad, but I need help identifying and figuring out how to fix the issue. She cannot currently get in the low bar position but we are doing the paul horn stretch to help with that. I told her to squat with what feels comfortable until we can reach the low bar position but even then she is in pain. Whats worse is that this person has squatted in the past (years ago) before becoming my client and did so without this pain. Here is her squat grip after unracking the bar and a picture of where on her arm she says it hurts.

Client form check - Album on Imgur

Any help is appreciated as I dont know if Im comfortable continuing to have her squat until she is out of pain.

Since she is basically squatting high bar for right now. Did you have her try squatting with her thumbs around the bar?

I'm not a coach but I suffer from shoulder and arm pain when squatting. Mine is a bit higher on the bicep. This isn't the video I saw but it's the same thing;
YouTube

That first stretch to stretching under the bar helped me to get into the low bar position early on. I now do it as part of my warm up. As HWC recommended above I wrap my thumbs around the bar and also widen my grip a bit.