You could ask her some probing questions and also offer her some education. As several posters have pointed out, a 3 month old (heck, any aged baby) who wakes only 1-2 times a night sounds like a dream.....heck if my 18 month old only woke 2 times a night I'd be jumping for joy.
Some examples of conversation starters:
- What has made you decide to start sleeping training? (Is it outside pressure?, unrealistic expectation of how often 3 month olds tend to wake?, some book she is reading?)
- Are you aware of what is considered normal sleeping behaviour for a 3 month old? (explain how their tummies are tiny and they need regular feeds, that it's normal for bubs to need a nightime cuddle, that waking 1-2 times is actually pretty "good" for a 3 month old)
- Are you aware that "sleep trainers" do not recommend sleeping training until bubs is at least 6 months old. (Not that I in any way endorse his work - but Ferber himself does not recommend sleep training under 6 months).
- Are you aware that many early childhood professionals advise against leaving a baby to cry alone - and they believe this can cause long term emotional harm to the child? (refer to Dr Sears, Pantley etc)
- How do you think you would feel if you were upset and crying and your DH/DP ignored you?
- Remember that she will grow up quickly and will probably start sleeping longer stretches on her own without any intervention from you (to be honest, who the heck knows how this will pan out, but it may help to give her some positive reassurance that her baby will sleep better on her own soon....of course as a sleep deprived mama of an 18 month old who wakes every 2 hours I'm still waiting for this day, but it sounds like her bubs is one of those babies you hear about that sleeps longer stretches).
- How do you feel when you listen to your baby crying out for you? How do you think your baby feels crying out for you and no one comes to her?
When all is said and done, if her mind is made up there is nothing you can do to stop her. If you want to express your opinion you could say somethign like:
"To be honest, I don't agree with sleep training a 3 month old. In fact it mades me sad to think of your baby crying on her own, just wanting the comfort of her mamas arms and instead to be left alone to cry" - but once you've stated your opinion once that is all you can do.