Standard length of underlying AKA Foley catheter is 16" so females have alot "hanging out" as stated before messing and catheters is more risky, one way to help mitigate the risk is use abdication device ,it keeps the catheter safe from accidental tension and honestly when used by a female I'd you apply it to upper abdomen or thigh it will increase absorption and wicking of diaper if pointed up like a penis , I am in a wheelchair and a male incontinent, standard procedure is to point up well sitting it increases the ability of the diaper to do "diaper things" extending the usefull life , when laying down you point down center mass ,keèps you from leaking over the top , another absolute safe play is use a "closed" system having the foley connected to a drain bag, you can then open the bag drain valve into the diaper when as full as you chose to drain.
That said there's millions of ladies who are bladder and bowel incontinent who have no choice about mixing the two ( many women end up with continent diversions like having a drainage port installed in there belly button area to combat repeated UTI's, your health is yours to make decisions with and make safe play choices or not.
One key difference is a foley catheter is a bacterial super highway direct into you bladder normal secretions and anatomy doesn't make it as easy as foley, even without a dictation device you can tape the catheter to the upper diaper area keeping it out of any stool is "safer" than just leaving 14" in the diapers center crotch area .
A public service advice ,
My girlfriend uses diapers however she is hung in a toileting sling on her hoye lift ever morning for coffee and evacution if she has a bowel movement in the diaper it means her body is off schedule ,of course that means she has to sit in it, she has her aides working split shifts, early morning they toilet & change her,put her in her wheelchair midday she is alone and diaper dependent till her evening aide comes to change her and put her in bed for the night.
Lastly for softer stool use Miralax it will not soften and increase stool volume, another stimulant laxative can be used with it if you want to speed your elimination up but isnt requred, you can so alot with Miralax , from simply soften to thin pudding ,you can decide based on number of doses a day ,you do need to consume the required liquid ( each dose of Miralax is 17 Grams of powder in whatever you want to mix it in ,it is basically tasteless but needs the liquid to form a feel in your gut ,that is how it increases volume and decreases consistency .find the consistency you require ,starting with one dose every morning and increase slowly to multiple doses a day , then decide if you want to add a stimulant laxative to be completely without aby control .