it depends on the spacing used between the glass. there are vinyl sweeps that slide onto the edge of the glass similar to the one that should have been used along the bottom and actually top. problem with these are that they take away from the 'frameless' look even thought they are clear plastic. how long has it been since you had this installed? Here is a link that might be useful: vinyl sweep

Ug, that's NASTY! Is that natural slate or just a porcelain look alike? If it's natural slate, then I understand why they tried to correct the problem with a topical sealer (mistake) but natural stone of any kind shouldn't be used in a steam shower. It's too porous. If it's natural slate, then it all needs to come out, unfortunately. I think I might try to pop off one of the tiles from the bathtub pony wall and see what I could see behind that. That's not a water critical space to worry about, and it should let you see at least what the first layer of product against the studs in the shower is after you cut a hole in the (hopefully) backer board under the tile. You can see if there has been any moisture migration into that cavity. The other place I'd start doing some surgery on is on a wall that's on the other side of the shower. There's got to be an interior space in a closet or other room where you can cut a hole in the drywall and see what's in the cavity. Drywall is pretty easy to patch, and it could relieve your mind, or confirm the dire diagnosis that the sealer foreshadows.

Yes...marble in a wet room needs sealing. There are many marble experts (stone experts are different from tile experts) who will tell you the marble needed to be sealed several times BEFORE it was installed, and then several times AFTER it is installed. And then sealants are used at regular intervals for a few years until the marble has been saturated with sealant and doesn't "need" it any more. Obviously the "before" install is no longer an option. No worries. You simply have to find the RIGHT stone sealer and apply it as many times as required. Then allow it to cure (could be a while before you use the shower) - and off you go. Keep reapplying as scheduled (by the sealant manufacturer) and enjoy your very pretty stone. Because this has been sourced/suggested by others (who deal with tile and not stone), I recommend you find some stone/granite professionals and start asking questions about your stone. After speaking with multiple professionals in your area, you should get a handle on what is needed and what is FORBIDDEN. Yes...there are plenty of things that are forbidden with marble. That knowledge is SUPER important. Hopefully Joseph or the Tile experts will pop in and offer some strong recommendations for sealant.

What roarah wrote. If it's a remodel, it needs to be built as a steam shower from the studs out. Sloped ceiling, insulation, vapor barrier. Preferable a porcelain tile, not a natural stone that can absorb moisture. All penetrations through the tile need to be vapor-proofed; Lights, plumbing, etc. Steam generator unit gets sized to not just the volume of the shower space, but to the materials used to build the shower as well.