Agreed with [MENTION=13820]bpatters[/MENTION], There is absolutely zero point in keeping them separate. You could be actually doing more harm than good as it is much easier to bond an adult with a young baby. Waiting until Fluff is in her adolescent phase will make it harder on both of them.
Regardless to what you're seeing during short interactions, letting guinea pigs have play dates IS stressful. Every time guinea pigs meet they try to establish dominance, even if you are not witnessing this behaviour, it is happening. It's also stressful, especially for a young baby, to go from constantly having a buddy, then to just have them ripped away. I imagine it would be very confusing for them.
Myself, along with many other members, have had a baby pig grow up with a group of adults and there have been no ill effects.
Babies need an extra source of calcium, their bodies don't care which source it comes from, whether it be from supplemental alfalfa hay, alfalfa pellets or calcium rich vegetables. As far as unlimited pellets go, I haven't met many pigs who would truly eat more than 1/8th of a cup of pellets a day, especially a baby.
I urge you to reconsider, both of your pigs would be much happier being housed with each other. This makes your vet sound quite uninformed on the actuality of owning guinea pigs.