I know it may seem awkward but hopefully she will understand these were on loan and you invested in them it only makes sense you would get them back. I think the preparing for both genders is a good response. I think the due dates are so close she's probably not going to have the time/energy to mail all you need once her baby has worn it and may not outgrow the sizes fast enough. I hope she can sympathize as it would be unfair to assume you'd buy a new wardrobe the second time while she uses the borrowed set again. Good luck!
Andrea -SAHM to Sean 10-09, Owen 1-13, and married to my best friend!