So very sorry to hear about the loss of your last foal - do hope your mare will fully recover.
Regarding the foal - please think seriously about leaving it with your mare. Animals need to grieve too and simply removing a dead foal can leave a mare extremely upset and confused. She needs to accept that her foal has died, she will still have a strong need to protect her new child and if you just take it away, it is natural that she will get herself into quite a state (I do know that some mares will accept the removal of a foal with no problem, but IMO they are in a minority)
We carry the dead foal to the field with the mare each morning and bring it back with her at night. If you can put her in the same field as your other mares and foals - just as you would if the foal was living - it will help her. The other mares wont interfere - she will keep them away and they will soon realise the foal is dead. It may only take a day or it might take a week or longer, but soon your mare will move further and further away from her foal to graze, and eventually she will join the other mares to graze - this would be the day that I would return her to her stable without the foal and watch her. If she seems quite happy, then remove the foal from the field (out of her sight of course) and then see what she does when let out the next day. If she wanders off happily with the other mares, you can safely get rid of/bury the foal.
I know this will all take some time and effort and perhaps you do not have the facilities to do things as I have suggested above, but as long as you can give your sweet mare the time to grieve properly and naturally, then I think she will thank you for it.
I stress this is just my personal way of dealing with a dead foal and a grieving mare. I well remember the one time I did not do this - an older experienced mare had a dead foal that had to be extracted from her, she was well sedated and I thought completely out of it, so I removed the foal and got my g/son to bury it. Within an hour I had a still partially sedated mare going frantic for her baby, so stressed she was careering round her stable and getting in a muck sweat. G/son was sent to dig up the foal and having cleaned it off I gave it back to the mare. Peace!! She flopped down beside it and slept the rest of the day. But as she was an experienced lady it only took her just over 24 hours to accept that her foal was dead and she left him in the stable and went happily off into the field with her companions. I never made that mistake again!!
Good luck with whatever you decide to do.
Anna