A point to consider is how flexible option blocks are at the desired 6th form(s). In some cases, selecting FM at a 4th rules out some essay subjects because they are in conflicting option blocks; so worth understanding that.
So your DD will need to decide whether Politics has red lines around it even if it means foregoing the opportunity to take FM, or whether she is prepared to be flexible. For example, it is likely that option blocs will accommodate M, FM, Phys and Econ because, each year, some students are likely to request that.
Equally, FM is often only offered to those achieving 9 or 8 at GCSE Maths, so need to be clear as to DD's likely outcome in that regard.
My DCs did Maths, FM, a physical science and a humanity and really enjoyed the mix. To answer @clary, Geog is sometimes regarded as an essay subject (eg LSE), but often not (eg U of Bath); there are not essays as such in Geog exams, more extended 16-markers.
One of my DC seriously considered Politics A level and it does look interesting; worth downloading past papers to get a real feel for it.