Absolutely, try them with a bottle now; if any or all of them like it, you can give them a wee topup once a day and help the ewe.
However, if she's doing them well enough at the moment, you may find that none of them will take the bottle. Ever. And that she'll drive herself into the ground feeding them.
So if it were me, with a thin ewe and triplets, I'd take one (or two if you have no other companion for it, nor likelihood of any) off now and rear them on the bottle. You might otherwise end up with a sick or dead ewe, and/or one or two or even three dead lambs. (Ask me how I know.)
However, bear in mind that I am on an upland farm in north Cumbria, where even if we have a good year, the grass isn't much to write home about. The situation could be very different where you are.
Also, when you say 'on the thin side', you may not mean the same as I would. Can you express her condition as a condition score?