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From my experience, I would advise against buying one bunny. If you can't get a pair it is better not to bother; however, if you have bought one the sooner you buy a friend for it the better. I would say that every week you delay it will take 3 or 4 times as long for the rabbits to bond.
Her rabbit is still a baby. This isn't the time to get a 2nd rabbit even if she did want a second rabbit. Always best to wait until a rabbit is fixed and then let it choose a bondmate among other fixed rabbits.
Baby bonds don't count because they can easily fall apart with the onset of hormones. Starting with two babies runs the real risk of ending up with two rabbits that refuse to bond.
That aside, many (not all) indoor bunnies can be quite happy as single bunnies. I've had some that absolutely had to have a bondmate. I've had a few that actually seemed better as singles. Depends on the individual.