Fallout – How to do multiple quests in fallout shelter

No, it's not possible for dwellers to heal by themselves in the wasteland. However, dwellers heal all damage when they level up in the wasteland.

But I don't really know how much health they have, might be important she's level 36, has 7-S, 1-P, 10-E, 6-C, 6-I, 4-A, 4-L.

You said it yourself, she is not level 50. There you go. And because she has 10 Endurance, she hardly takes any radiation damage.

I try to max dweller stats before I send them out to level, so I have a level 8 dweller with 25 stimpacks and high +E gear and a big gun take about 2 days before they use the first stimpack. That's because with every level up their health and radiation will reset. In addition, if they have more than 10 Endurance, they will never take radiation damage (red bar).

I didn't have an undammaged dweller right now, but I think it's obvious that this guy would not survive 4 days with only 6 stimpacks without having some additional healing going on. I believe he was level 8 when I sent him out.

There's really only two options:

1. You are experiencing a bug as others have commented, you can contact support to report it, or start a new game (ugh, I wouldn't)

or

2. You are just ridiculously blessed by the RNG gods and sooner or later you'll get your first attack. Those are RNG based events, but I thought that over time the chances of getting one increases to the point where it's inevitable, but I could be wrong.

Personally I'd be happy with no mole rat attacks, I hate having to station people all over and not working in generation rooms or skill rooms.