If she is still only 210 grams, then one adult mouse is enough for now, but she should soon grow big enough to need 2. It also depends on the individual mice, though. Many pet stores sell "adult" mice that I would describe as weanlings, not truly fully adult yet. Your BP could probably eat 2 of those.

To figure out how much to feed her, there are 2 good rules of thumb. One is to feed 1 prey item that has the same girth as the largest part of her body. That works great for people who are feeding rats, and will always be able to find a rat of the appropriate size.

For people who feed mice, which don't get big enough to be a full meal for an adult BP, you can go by weight. This also works if, for example, you have a bunch of frozen rat pups that you want to use up before you order a bigger size. Feed prey items of the appropriate weight & size to add up to about 10-15% of her body weight at each feeding. Since she is 210g right now, that would be 21-31.5g.

Feed once every 5-7 days when she is little, and 7-10 days once she gets bigger. Also, since you say she will be only a pet, she will not be using up lots of energy & resources producing eggs, so you can stop increasing her prey size once she stops her rapid growth. She will continue to grow gradually throughout her lifetime.