What size nipple should I use for granny bike rim?
5.5mm spoke holes sounds ridiculously large and it would not surprise me if that's not correct. Ryde don't mention it on their generic V38 page nor do "Flying Pigeon" on their Westwood listing but they do suggest 2.0mm spokes. No mention of needing large head nipples though.

If you can try the large head in the rim before buying definitely do that. Otherwise I'd be tempted to wait and see, since if you need the large head nipples you'll need to buy them separately anyway so you only lose time by waiting to see if you need them.