NFC have a large minimum order - 20kgs, i think - so if your daughter has a very small flock and you didn't want to mix it with fleece from other flocks, you'd either need to store up a few years' worth, or get the processing done otherwhere.
Both Griffiths Mill and Halifax Mill will take smaller quantities.
You'd need to make it clear you want the yarn for weaving. I'm not sure whether any of the three mentioned make a worsted yarn, which would be preferable for the warp, but if they know you want to get a blanket woven, I assume they would be able to make half or all of the yarn higher twist, and therefore stronger for the warp.
I would imagine you may well get offers to weave the cloth, for a fee of course. Might be best to ask on UK Weavers on Ravelry, unless your chosen processor can recommend someone.