Introducing new baby bun to older bun

Our 10yo twins have had bunnies, Darwin and Cookie for 2 years.
We were devastated to lose Darwin a few weeks ago from stasis.
We made the decision that we would have to get a new companion for Cookie. We got Poppet on 13 May. We had her vaccinated and then began introducing the buns for a time in the outside run (the shed is divided in 2 still). The first could of days were super and they have been snuggling up.
There is no squabbling, but Cookie (neutered 2yo Netherland Dwarf) started trying to mount Poppet (mini lop). She didn't seem too bothered and could get away, but I have separated them. My concern is that he could do damage to her either from his weight (though he's not a big chap) of trying to mate with her.
I would appreciate any advice on how to deal with this please.
She will be neutered as soon as she's old enough (for health reasons as obviously, Cookie cannot reproduce).
Thanks.
Jo

I don't know how to add a photo to show sizes.

[video]https://photos.google.com/photo/AF1QipNv8yKYap_RI4sZJ7KnQ7FQjgTWbNafpAoqO73P[/video]

The photos aren't working. There are guidelines in the Help to Use the Forum. Mounting is normal so he will do that whenever you put them together until they settle down. Even when she is neutered there will be mounting at first. So it is up to you as to whether you are going to keep them separate until she is a bit older or put them back together. I am sorry you lost one of your rabbits.

If you're posting from Google Photos you'll need to use the tags with the 'share link' option ...g link doesn't work as it changes every time.