If there is a big size difference I would wait until she is a bit older and can be spayed. (edit: just read on the other thread that she's only 7 weeks or so - in which case there's no way I'd do it now; youngsters are at extremely high risk of developing coccidiosis - which can kill - when they are exposed to stress and being taken from mum and littermates, new home and big bunny wanting to eat you will be too much for the little mite).
The "48 hour" technique isn't really 48 hours, it's more that you need to be able to devote 48 hours to pretty constant watching (including sleeping next to them), and be available for several days afterwards to keep a very close eye. In many ways it's absolutely no different to bonding in a series of short introductions - except that instead of being separated and having to go back to the beginning every time you put them together, they work it out all in one go. Personally, whilt it will be stressful to the buns, I think it is far less stressful overall because it is over and done with more quickly and they do (usually!) settle down quite rapidly over the course of the first day and night even if it takes several more days before they actually bond.
You say that when you put them together the second time they 'circled'. I would not let bunnies circle each other while bonding, it is almost inevitably going to end in a fight and possible injury, so if you see the signs that they are going to circle each other, gently pull/hold them apart for 10 seconds and then let them go again.
I wouldn't use a crate to start with as you might not be able to access it quickly enough if they do fight - you can use one after a couple of days when things have settled a bit, but I would just use those panels that are used to make a pen (or block off an area about 4ft * 2ft with something, but keep the top open). Another thing to consider might be to see if there is a rescue near you who would bond them for you in return for a donation, or there might be people here who live nearby and could give you a hand to at least get it started
Have a look around in the 'behaviour and bonding' section in the 'rabbit care discussion' part of the forum - you should find plenty of good advice there