Infertile gilt? Need advice!

Small homesteader here. We got three Idaho pasture pigs this past spring. Great pigs all around. Such nice temperaments and easy to handle. Our boar bred one of the sows early on. She had her first litter with their previous owner and second with us. No problems. Great Mom. We also got a gilt. She has been in with the boar since April and still no apparent pregnancy!
I noticed their first two heat cycles and then nothing for a couple months. Figured she was bred. Gestation came and went and no piglets. I have been moving them around our pasture and so the last few months have been further afield so it’s possible I could’ve missed her in heat. However, I’ve seen the last two cycles and watched the boar. He doesn’t seem to be having trouble and we know he’s fertile since he sired the last batch of piglets from the other sow.
Our so far impregnable gilt is the same size as our other sow. She is very healthy and is seemingly more active than either the other sow or the boar. She would be about 2 1/2 years old now.
Any ideas what could be going wrong? Any advice on what to do? My one thought on it was that I could separate them for few cycles in hopes that the hormones might prompt them to breed more intentionally?? One cycle? More?
I tend to get attached to our breeding pigs so I don’t want to cull her without trying everything.
Thanks in advance for any advice.

Misery loves company.  I have a similar problem with one of my KuneKune gilts.   I have little knowledge of value to share, but I will be watching this thread with interest.  Thanks for the post.