She is very much mistaken as the mark on the top left corner of the stamp is from a first day issue postmark (Mr. Tickle).
She also says she buys stamps off ebay. Shown below, this was the first picture of hers I noticed on the group.
You can clearly see postmarks. Nice for a stamp collection or for decorating letters/scrapbooking, but no, she uses them for postage. One of the group's moderators agreed they were postmarked and that it would be fraud to reuse them for postage.
She didn't listen.
The pear from the tasty stamp issue is on the top envelope and could well be the same stamp in that all used stamps picture. The same first day issue postmark is also visible on the two Mr Men stamps. In the thread discussion, she says:
Further investigation into her posts in the group reveal another visibly, but faintly, postmarked stamp across the bottom part of the neck by the 1st indicator..
I can perhaps forgive a one-off mistake, but this is ongoing.
The black scrub-out is mine as I don't want to show the names of the unfortunate recipients who may have to pay the surcharge for the sender's criminal behaviour.
Royal Mail's postal fraud online form isn't particularly helpful in this instance.
On the incoming front, yesterday, I received a letter from the US - the stamp had sticky tape on. You might just be able to see the different colour paper underneath the stamp on top of the envelope.
I peeled the tape from the envelope and revealed this - it had been used. The angle of the photo doesn't do the gold paper justice - looks like it is from an envelope to go with a greetings card.