How to handle a friend who seems to compliment me just to knock me down a peg when I deflect

A close friend of mine of many years and I have this three part interaction that I never really know how to handle or why she does it.

First, she'll give me a compliment she knows will make me kind of uncomfortable. For example, she recently said something like "you're such a good person for doing volunteer/mutual aid work", which is something I just genuinely believe we should all be doing for each other at least a little, that's part of healthy community and society, and I've told her before that that kind of compliment makes me uncomfortable. Often, these compliments come out of nowhere, like we weren't even talking about volunteering in this examples, it just came out of left field.

Then, I deflect a little, like in this instance, I replied like, "I'm just doing my thing and wish I could do more."

Finally, she immediately shoots back a disparaging remark like, "I didn't say you were a SAINT, jeez, calm down!" Her demeanor goes from complimentary to mocking in an instant, and I never really say anything back, either I change the subject or she does.

She only does this in front of other people, I should maybe mention. When we're hanging out one on one, she doesn't usually give that kind of compliment, and if she does and I deflect, she doesn't react the same and will often even encourage me to be more confident in myself. So it gives me a bit of whiplash when this happens in a group setting, and I don't like making a group hang awkward, so I just push past it as quickly as I can and brush it off, but it does hurt my feelings and kind of feels like she's intentionally trying to knock me down or something, though I really don't want to believe that of a long time friend who is otherwise usually sweet and supportive of me.

I'm planning on just asking her the next time this happens why she does that to me, though the thought of potentially starting a bigger conflict in front of others is daunting and I'm not sure if I should pull her aside or just talk to her about it one on one instead, though my gut for some reason is telling me I should be direct when it happens in front of other people. Is that too aggressive or unnecessary?

Any perspective anyone can offer or advice on how to better respond either to the initial compliment or to the following shut down would be very appreciated.