Welcome to HTW...!!

There are several load range "G", 16", 14 ply tires built in Asia in a 235/85x16 size and one built in the U.S. http://www.goodyear.com/cfmx/web/truck/line.cfm?prodline=160007

I got a set of these G614RST's that are coming 7 years old, they look like new, but, they're 7 years old, time for them to go. Called the local GY dealer and got a quote of $405.00 each. That's tax, mounting, balancing, the whole works. $405.00 per tire, that's not good..... The G614 is rated at 3750# at 75 mph. The casing is regroovable as well as retreadable. If your trailer is stamped for 10 ply load range "E" tire, I would look closely at these 2 steel brands/models I've listed below. They are rated at 3042# at 99 mph or faster.....

http://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=XPS+Rib&sidewall=Blackwall&partnum=385R6XPSR&tab=Specs

http://www.tirerack.com/tires/tires.jsp?tireMake=Bridgestone&tireModel=Duravis+R250&sidewall=Blackwall&partnum=385QR6R250&tab=Specss

This 10 ply GY Marathon is rated at 3450# at 65 mph... http://www.easternmarine.com/goodyear-marathon-st235-80r-16-radial-tire-load-range-e

Then there's the 14 ply tire built in China, Asia, etc rated at 3750 at 65 mph.  http://www.easternmarine.com/trail-america-235-85r-16-lt-heavy-duty-tire-load-range-g

For your trailer, I would look hard at the Bridgestone R250 with the all steel casing, similar to that of the XPS-Rib, G614RST and the M895.

Some propaganda from Carlisle via Discount Tire...  http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos

Your rims will have a part number/model number. This number would indicate what the maximum weight and or the maximum air pressure is for the rim.... The maximum weight and or maximum air pressure may be stamped on the rim itself. Depends on the mfg. Quickest way is to check with a reputable commercial tire shop in your area, have them take a look before ordering your tires. A 14 ply can be run in place of the 10 ply on the 80 psi rated rim, just have to run it at 80 psi which gives you a 3042# rating, same as the lrE 10 ply tire. What is stamped on the serial number tag? What is your gross axle weight rating for each individual axle? 6-7-8000#?  My trailer has 2-8000# axles, but has a GVWR of 18500#. Mfg. is figuring the truck is going to carry at least 3500# of pin weight. That leaves 15000# for the tandem axles. Remember, 4 of these 14 ply, 235/85-16 tires only give you at total rating of 15000# on the tandem axles even though the axles are rated at 8000#. 4 10 ply of the same size give you a total of 12168# total capacity for both axles. I'm rambling....

Happy New Year!!

While you can run 14 ply tires at 80 psi on wheels that are only rated for 80 psi.  It's probably not a good idea.

You mention your daughter will be hauling this trailer. The risk is too high that she or somebody helping her will look at the tire sidewall, see the 120psi rating and try to inflate to that limit.  Over inflating the rim.  The numbers on the tire sidewall are MUCH more visible than any stamp on the metal rim.