Any tips on helping hair regrowth?

So as some of you know, Roxy had to go to a heart specialist to get checked out, although she got the all clear she's left with 3 bald patches from where they did their scans.
It's been 6 weeks now and there's practically no regrowth of the hair.
Now these are pretty dodgy places for hair for some dogs but she's a hairy dog, the patches are under each armpit and on her underside where the rib cage meets the abdomen. I've seen other dogs that have hardly any hair in these areas but hers are usually quite covered. This is causing an issue with her harness, it's rubbing under armpits and the skin looks red and sore, any tips would be much appreciated!
I would just walk her with her collar but I really don't trust them, especially with her, she's wriggled her way out of them before!

I don’t know what would help hair growth but would something soft wrapped round the harness help at all?

I use a 'Trixie' harness with a couple of my dogs, they are fleece and padded, may help if it's the right style of harness for Roxy. You could also try Sudocream on the sore patches, double check that but sure it is safe for dogs. I would use vaseline with a drop of lavender myself, but that's prob just me! Ps Glad she's had the all clear

How about a herbal supplement? I've been giving Harri Billy No Mates as a flea and tick treatment but it's had the side effect of giving him the most tremendous thick and glossy coat. The difference is really noticeable.

I always massage tea tree cream into bare butt patches on greyhounds we have fostered and that seems to work well.

@Josie that may help yes, thanks for that suggestion, although I don't really have anything :/
@Flobo I think I know which harnesses you mean, the thing is she's just got a new harness! It's a front leading one which was really helping with teaching her not to pull but it sits right where the patches are. I am now using her old harness which doesn't sit so far forward which I think is helping. And thank you I'm very chuffed!
@Caro Perry I will consider that, that's interesting!
@Ragsysmum thank you, I didn't think of creams as I automatically thought she'd lick it off but of course it could be tricky to lick her armpits so that could work!
Thanks everyone

Good old fashioned olive oil massaged in can help. I do wonder if what you actually use is less important than the massage itself which stimulates the cells and small blood vessels under the skin.