Josiesmum This is the problem I have
Obviously she is not getting anywhere near enough elemental iron. If she was able to take Ferrous Fumarate each tablet contains 65-70mg elemental iron compared to Gentle Iron's 25mg but the constipation would be even worse.
What I have done is to tackle the constipation in a couple of ways, some may be suitable for your daughter, mix and match if necessary:
For a laxative effect (which isn't the best solution long term):
Vit C, however much it takes without causing upset tummy. I take L-ascorbic acid powder (I use Nutribiotics) made into a drink with orange juice. 1000mg at a time, three times a day (it can be more). Dr Myhill recommends 2000mg ascorbic acid at bedtime to produce a bowel movement the next morning. It will be obvious when bowel tolerance has been reached.
Magnesium citrate (again I use the powder form).
NutriAdvanced Psyllium & Apple Pectin. This is fibre so gets the gut working rather than being a laxative lifestyle-labs.com/products... ( I have it on Subscribe & Save to make it cheaper, you can cancel at any time with no problem). I don't need as many as it says on the pack.
Psyllium husk is a possibility but that tends to be rather gloopy and not always easy to get down.
Linus it Gold is another possibility amazon.co.uk/Linusit-Gold-G... Some people grind the seeds.
Ortis Fruits and Fibres dolphinfitness.co.uk/en/ort... Be careful to ensure it's that one, it doesn't list Senna which the other one does.
Also look at probiotics. There are many different strains which all do different jobs but here's an interesting article constipationexperts.co.uk/b...
So there's a few ideas for the constipation.
For the iron I have started to eat liver regularly. Not something I've done for many years and probably wouldn't be my first choice for a meal, but nicely cooked I now eat it about once a week and my ferritin level is now rising.
I hope that helps in some way.