Well then, if you're so sure
she's in foal why did you even bother to ask?
You need a vet out to see her as she's obviously still horribly underweight, and having a foal without medical intervention could very well kill her.
Those pictures don't prove she's in foal. If she'd been bred heavily when younger it's likely the first place she'll start showing weight is in her belly, as those muscles are sprung.
That 'white stuff' dripping from her vulva could be from a uterine infection. Healthy mares in foal do not have anything dripping from their vaginas, and not going into heat proves nothing. Many mares stop cycling once they hit their middle to late 20s.
Again, get a vet out
. He/she will be able to determine for sure whether the mare is or isn't in foal.