Once you buy the poses, they are yours except to use them, you have to have a valid premium subscription.
When your premium subscription runs out, all your purchases become locked.
You can continue to play for free but with only the free user items.
Ask her to check if she is still a premium payer. Her poses and other purchased items will be restored once she has paid to become premium again.
If she is premium and the items are mysteriously disappearing, this will be a glitch.
Ask her to check her Achat account on the web to prove when the items were purchased and take a screen shot.
Then report the matter to Achat through “Support”
Please let us know how she gets on.