There is no magical formula for babies/toddlers. They sleep through when they sleep through and all babies are different. Mine slept through (last feed at 10:30-11, waking up around 5:30am) at 8 weeks. Other's don't until they are 2 or even older!
I think if your DP is happy to feed, she should be able to. BF is a very special and close relationship and she and baby BOTH need to be ready for it to end. Mine ended way too soon due to many issues from both baby and my low supply, and I am still sad about that 2 years later! So while I can understand that you are tired (and hopefully also thinking of your DP being tired too, not just yourself), until she is ready, IMO she should keep feeding, and feel she has your support to do so.
I was going to suggest the same thing as a PP poster. If you are not getting enough sleep because of it, could you (or your DP) sleep in another room from Sun-Thurs, or even a few nights a week so you can get the sleep you need, but she also gets to continue her BF relationship until she is ready to wean, or bubs self weans?