Error discovered after posting international parcel

[dragonsmail]

My elderly neighbour commented today that she'd been surprised how little her annual parcel to the USA had cost her to post. She said she'd only paid £3.20 whereas it usually cost a lot more. This rang a few alarm bells for me and I asked if she had a receipt.
Looking at her receipt, I can see she's been charged for a Small parcel, First class to UK. (although the parcel was definitely correctly addressed to her friend in the states.) She didn't notice if an Airmail sticker was put on it at the counter, but I'd assume not on the face of it.
As she posted her parcel a couple of days ago, it was much too late, to go to our local Post Office and ask about it today.

My question is this - what is your best guess about what will happen to this parcel? My neighbour is rather concerned. Alhough she herself have access to the internet, and email etc, her American friend doesn't, so she can't let her know what's happened.
Thanks in advance for any thoughts!

[Lounge Lizard]

Normal procedure for underpaid overseas items is for them to be returned to the sender, so it will be most useful if she has put her own 'return address' on the parcel.

[dragonsmail]

I have told her always to put a return address on any parcel, so hopefully she will have done so this time. I do hope you're correct and she gets it back, thanks.

[dragonsmail]

This parcel hasn't been sent back yet, should it take this long?

[TrueBlueTerrier]

This parcel hasn't been sent back yet, should it take this long?

It may be that as it was a Post Office error and they perhaps used a Horizon Label, then the Post Office has taken the hit and sent in onwards. Check with the receiver they may have got it.

If not, then no it shouldn't take this long, if there was a return address.