Combine 3 separate accounts

-- url of the page with the problem -- : httops://pearblossomfarms.com
-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.5.1
-- PHP version -- : 5.5
-- Error-message(debug-mod must be tuned on) -- : N/A

One of our customers opened 3 different accounts and submitted orders with 2 of them

Account A: 0 orders
Account B: 1 order
Account C: 3 order

Naturally, she wants to keep account A which has no orders. What would be the best way to approach this? She wants to also keep her order history so just deleting the extra accounts won't work.

I was thinking of doing this:

In account C change Username and Password to reflect same user/pass as account A (the one she wants to keep)
The I'd delete account A and I only have to deal with 2 accounts.
How would I transfer the order made under account B to account C?

Or is there a better way to handle this? Can accounts be merged? Can I move an order from one account to another?

I don't mind getting my hands dirty in the database if I have to. I have done it before many times but I don't want to break anything.

Thank you very much. I have never used the mass actions, but I'll build a clone for testing and see how they work (and make lots of backups)
I should have thought about it.

Thank you. It worked like a charm. Great feature.