I wanted to ask if the backrest can be put in a straight position for the baby to stay, with a straight spinal position? It always seems like she doesn't stay as it should because the angle in it isn't right.
Thank you in advance.
Unfortunately, no, not really. Many - mainly lightweight, but not only those - pushchairs have a slightly (or very much) slanted position and some kids or moms just need a stroller with an upright position. Not all strollers offer that.
One other thing parents do is putting a belt or any kind of strap behind the backrest and securing it around the bars under it to hold the backrest more upright. This is NOT POSSIBLE with the Mara buggy, however, because it is not a strap = looser recline, but it is a lever-operated one, so there's no way a strap would do it (the mechanism will not allow it, I believe).
The only things possible here are either the child getting used to the seat or a stroller change. Try classifieds where a mom maybe looks for swapping her stroller... or sell yours and get a Chicco Goody with a more upright seat instead (Chicco Goody long-read stroller review can be found here).