It depends on the baby - how big they are, how strong, etc. I have run the gamut with 3 babies. My first son was born preemie and tiny, I wore him on my front for months. My last baby, born this past Feb, was so big he killed my neck within 3 months. He weighs over 23 lbs at 9 months and is too tall to wear on front (he is over 100% percentile for height).
Having said that, the only front pack that works is the one that fits you and her both - no matter what anyone else says. For example, everyone loves Ergo ones, I bought one and hated it - my back injury couldn't take it - and all my babies wanted to look outwards by 4 months time anyways, and you can't with the Ergo. Where as, for us. a high end Bjorn worked well.
If you do hike with a baby in the front, use trekking poles - you can't see your feet.
And make sure they are wearing a bunting or similar, they get cold fast. Take them out every hour or so to stretch.
I use something called a Sammy Sack, which are made in Seattle, to go over the babies when front wearing (I also use it on their Bob Jogger stroller).
If anything at lest go outside with her and push a stroller around - at 3 months a stroller that takes a car seat is great. You won't want to do bumpy stuff for a few months more, but at least you get OUTSIDE.
Having said that, I took all 3 babies hiking at young ages. Once they can be in a back carrier life is easier. It goes fast though. I wear my youngest in a Deuter III pack (I have the Deuter rain cover as well which covers 90% of the pack). I won't lie, it isn't light. But it rides well. Cheap packs rarely ride well with kids.
PS: Now that we have a toddler (2.5) and a baby (9 months), I rely on my jogger more for getting out. I find if I get fresh air life is better. The toddler can walk nearly 3 miles now but I don't like taking them out with just me when hiking.