I think she’ll have to talk to a midwife or Ob about those specifics. I’d think that again, it would be anything that qualified her THEN as high risk. Sudden spike in BP? Increased risk, therefore a decision must be made about the situation, but depending on the severity of the change, it may or may not be significant. But that would be managed at the time by the health provider (unless she’s going unassisted, in which case, I hope she has more info than I do!). Any of her vitals being out of normal range would be questionable, I’d think (temp, BP, heart rate, respiration rate).
Ruptured membranes - happens all the time in water birth, and they don’t take you out. However, they may ask that you not get IN until labor is definitely underway if they’ve already ruptured. A long soak can reduce oxytocin production, so that will then slow the labor. Don’t want to jump in immediately and slow things down more if you are technically ‘on the clock’ with ruptured membranes and no active labor.
Bleeding - bloody show is again, normal. Any big gush of blood would need to be checked out, as would symptoms of placental abruption without bleeding. But normal bloody show isn’t an issue at all.
According to my handy “The Birth Partner” laboring in water is great, but should be limited to 1.5-2 hour stints, since hydrostatic pressure can affect the production of oxytocin, and slow labor. But there are no listed contraindications. So a slow labor is a contraindication for getting in just yet, and in general, waiting until 5 cm dilation is best…
Really, anything else that would qualify as an emergency/risk would probably disqualify her for water birth… but all those are the same things she should already know from her care provider. Things like prolapsed cord, excessive bleeding, maternal fever, being infected with dangerous bloodborn pathogens (positive for HIV, say), footling or transverse breech presentation (or any breech presentation, depending on the provider), fetal distress, substantial meconium staining in the fluid (might only necessitate increased monitoring and getting out of the water so that baby’s nose/mouth can be suctioned before full delivery), and so forth. Try here or here for more.
Question - does the DIL not have someone guiding her on this info? Or is she just not sharing the info with MIL?