Thanks for all your answers, wasn't expecting for answers this quickly.

@meet.vino : I can't say I'm a big fan of Sailfish OS, even if in this case I could buy a tablet with this OS, but I would rather buy something that is actually on shelf and asap, so waiting for them to get the targeted sum and to produce it, is not an option.

@biketool : was thinking about the Nexus 7 as it thicks all the requirements, but I can't seem to find it new on the market (if you know where I can find one please let me know).... don't need telephony, only data over 2/3/4G

The phone she uses right now is a Nokia Asha (can't remember the model) so I think tethering is not an option. And I would rather have something with build in cellular data.

So, what currently available tablets have the specified requirements.

PS : found a Nexus 7 here, but seems kind of expensive for a 4 year old tablet.... don't get me wrong, if I find something that really worth spending that amount (or even more), maybe I'll do it....

Does it really have to be new? I'm sure you can get one second hand in near mint condition for a fraction of the price.

So the weakness of the Nexus 7 is the screen cracking. Get a nexus 7 2013 with a cracked screen for cheap and buy the bezel, LCD, and digitizer; then replace those parts and you have a working machine for cheap. then add the protection I listed above. The big downside is that the Nexus 7 like most newer phones and tablets lacks a SD card slot.

I tried to replace the screen on a N7 (2013). Not as easy as it looks and not that cheap either, I ended up messing it up trying to remove the old screen (it's all glued so you have to use a heat gun and I wasn't careful and melted some plastic).

Decent tablet though, I have the LTE variant and it's currently running LineagoOS. The one I tried to repair was someone else's.

Agreed, I suggest a new bezel vs heating and scraping, took me 3-4 tries at trying to be cheap recycle stuff before I just got a bezel and a new LCD and digitizer and assembled them. but it is also possible to get an assembled bezel with the digitizer&LCD all together. Just pry apart, disassemble, and plug in the two ribbons. I think it is the price of broken tablet + ~$50US.
If you are trying to recycle the bezel then be careful not to melt the plastic as it will become impossible to properly seat the glass digitizer.
then come s the crack and no more digitizer though the LCD still works and you can use a USB mouse. I found stripping the adhesive proteceion and placing the lcd-digitizer face down and then alligning the bezel/frame over it worked best for me.

I put Lineage on my wifes Yoga 3 10" and it works great.
Also changing digitizer is quite easy as the frame is easy to disassamble.
Digitzer did cost 25$ and twoo weeks wait from china, including some not working UV Glue that cost me an additional evening to remove the **** again and reglue with pattex 100%

My girlfriend's birthday is next month an I thought that the tablet could be her present, that's why I would rather get something new (don't think a second hand tablet will have the same effect...).

Plus I am not really a hardware guy, so would be difficult for me to replace anything on a tablet.

It is a shame that none of the currently available tablets is supported by Lineage OS...

I've got a SM-P600 (Samsung Galaxy Note 10.1 2014 Edition). Ok, it's rather old but what I like is the pen which is pressure sensitive (Wacom digitizer). That's the reason i bought it (used but great condition). I like how you can use it as pointer and navigate with it through web sites, even those hoverable dropdown menues. The battery life is really good. There's a LTE Version as well.

As I've seen, theres "official" LineageOS available for it. I'm really thinking about giving it a try.

Does the Jolla tablet actually support that option?
Both hardware-wise (USB OTG with enough power) and software?

What I would really like is to be able to use a normal x11 environment in my Nexus7; or any new tablet or phone I get. That and be able to use regualr bash scripts and commands without figuring out the irritating differences. The difference is sometimes like having to jump into a DOS prompt after 20 years on linux /unix.
Ideally I would like to see a nicely designed Maemo5 type multitouch environment GUI.