gap patch between shower walls

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I have a shower pan (plastic?) and 3 walls with tiles. I am cleaning some old caulking along the tile walls and shower base. At the gap of two walls connecting and close to the shower base, I remove the caulking too hard, so I pulled out some harden white piece (I guess it is old thinset), the more trouble is that I "scooped" a narrow piece of the green drywall out.

I plan to put some thinset back into the gap and caulk it. Does it sound ok?
Thanks

joecaption

Without a picture it's hard to say.
#1 It's never a good thing to have sheetrock in any wet area, sure it's not failing?

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sorry I do not have picture now, but I am pretty sure there is green sheetrock behind the tile. I think it is from the builder when the house was built in 1989. But I do not redo the whole shower. Initially I just want to clean the old caulk and recaulk as a maintenance.

joecaption

As long as the tiles are still firmly attached and there's no mold that keeps growing through you should be fine.
Any I see that old with just sheetrock are falling apart.

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The tiles seems to be sound right now. I will go ahead to fill the gap with thinset and caulk.

Thanks