I go with the "half your age plus seven" rule for age gaps. Anything outside that range us officially creepy!
For me the context doesn't make it less weird. I think I can see the reason for the relationship being partly due to trauma- after everything she's been through, she gets attached to the boy. But I still find that being framed as romantic squicky. The switche up with the kid is interesting, but also makes me think the reasons the relationship will be written as unhealthy will be more due to that than the age gap? (Not saying that's what you'll do in the actual story, just surmising from the blurb we have to go off of)
At the end of the day I just wouldn't be interested in reading such a couple, but it sounds like they're less a feature than part if an ensemble cast from your comments? So if the focus of the over all story isn't their relationship, you probably won't be at as big of a risk for alienating readers who don't like it. Then it'll just come down to how you weave things together.
Sorry, don't know how helpful all that is. XD