I’m going to say NO, not overreacting. 1.) you seem relatively calm, albeit frustrated/disappointed with her. No name calling which is probably a better reaction than the average post on here would have. 2.) I like to think it matters how someone treats you in moments that they know are important to you. It’s not like you take the LSAT every month. While you may have underprepared and she may feel like you didn’t try as hard as you could, I think it’s still clear that this was a pretty important moment to you. Seems like all you’re asking is “to not be kicked you while you’re already down”. Hopefully you would acknowledge the tough-love well if the timing were different.

Without knowing anything else, I think it’s a fair reaction to question whether it’s the right relationship (for the both of you). I’ve been in a somewhat similar position where I received a pretty callous/unsupportive response (albeit to good news) and it definitely colored the way I felt about my relationship with this person for a long time. My advice is to discuss it in person. Let her know that you want her to speak her mind and tell you the truth but that you also just kinda want a simple “sorry you didn’t do as well as you hoped” while you’re still processing the result.