It massively depends on what the situation is, and specifically, how low your baby is.
Doctors gauge this by a theoretical line between two bony prominences inside your pelvis (felt during a vaginal examination) - the "ischial spines". If your baby is distressed and needs delivery, even if you're fully dilated, it will be a CS if the top of the head is above this level.
If the head is well below this level, it is well down in the pelvis and should be delivered vaginally (I.e. ventouse or forceps if natural isn't happening or baby distressed) because it will be a traumatic, difficult, dangerous caesarean, for you and the baby, with a big risk of bladder damage and serious blood loss for you and skull fracture for your baby. If your midwife thinks that in this situation, the baby's head can simply be pushed up to make a caesarean easy, and that this would be in any way a good idea just to avoid forceps, I'm afraid she's clueless. We do ask someone (usually an experienced midwife because of the risk) to push up on the baby's head, but only because otherwise we may not be able to deliver the baby, and the push-up itself comes with a very real risk of skull fracture. This is not something I would recommend you ever choose.
The in-between grey area is trickier and your preference may come in to play here. If the baby's head is essentially at the level of the spines (and it's not always an easy assessment to make), there is a choice to be made - do they attempt a forceps delivery, or go for caesarean? You may be surprised to hear that obstetricians will tend to be pretty conservative and go for a CS if they are in much doubt - because there is not much worse than failing to deliver with forceps and needing to do a CS anyway.
If they examine you in theatre and choose a caesarean, then yes, they may give the baby's head a little nudge upwards just to raise it a centimetre or so in the pelvis and make the CS that bit easier. But this is a different kettle of fish to the emergency push-up done when a baby low in the pelvis ends up delivered by CS.
If not done for fetal distress, the usual other reason is a malposition - the baby is back to back or looking sideways. Again, if this has halted the labour before the baby crosses that imaginary line, it will be a caesarean. If it has already crossed that line, trying to turn the baby and then deliver vaginally would be better. If it's hovering around the line, it will be the obstetrician's opinion on the safest method, but your preferences may well sway them too.
Unfortunately, no one can tell if things are going down the route of needing forceps, so we can't do a CS "before it's too late". You need to be fully dilated before forceps can consider being used, and once you are, it will all be about the position and station (level within the pelvis) of your baby, which will be very specific to each woman's individual situation.