Oof. You need to set clear boundaries for sure. If you don't, she's going to lose you the hard way (you'll get so burnt out you just stop existing in her life) and she might honestly have no idea how much this spamming you affects you. If she cares about you at all, she will hear you out and try to be receptive.

If she doesn't care about you and thus can't accept a healthy boundary, then she's toxic and you do need to consider cutting her off. She expects you to read and respond to everything, no breaks, etc... What the heck? That is not even close to reasonable.

Hoping the best for ya. Kudos to you for putting up with it at all, let alone as long as you have, but at some point your mental health needs to be considered.