Hopefully fixed for the next release.
This one is an odd one, but I though I think I've ironed it out to work as intended. The bug was that right after she gave birth, Jana was supposed to go on Sterilex. In code, she would gain the "Infertile" perk, which makes her both not-fertile and not-virile, instead of the more-correct "Sterile", which should make her not-fertile. This would explain your bug of her not being able to get pregnant or get your character pregnant.
However, to add to that, her creature script is not marked for serialization, so even if she did gain either perk, saving and reloading the file would reset her character values, so any perks she did have last time wouldn't have carried over. So if you saved after she gave birth and then restarted and reloaded your save, her "Infertile" perk would no longer be there, so you would be able to impregnate her again, as well as be impregnated by her. This is obviously not as intended since her giving birth is tracked and she'll mention being on Sterilex due to that.
So my fix is to replace her redundant perk gain and instead set her Sterilex mode with a flag. Once she's on Sterilex, it should no longer be possible to get her pregnant again (unless there is a future event that takes her off it, so the flag can be reset again). But she should still be virile and able to inseminate the player character and cause them to become pregnant--which I think is the initial intention. Any old saves should have her Sterilex automatically applied when asking her for sex (if she's not currently pregnant and has given birth before).
When testing the fixes for this bug, I also patched up some other weirdness and made sure the result was consistent. I also noticed that since you'll never see her pregnant again after she's on Sterilex, I've made it to where if your game has Silly Mode enabled, and your character has inseminated her with a total of 5,000 mLs of fluid or more (this value will also be tracked), her bust image will switch to her pregnant variant. The amount of cumflation will cap out (10,000 mLs) so she's not forever stuffed, unless you keep filling her up that is. But under normal conditions, her cumflation will gradually reduce over time (0.5 mLs/minute) and her image will eventually return to normal.
With that, hope this helps.