If the EGR is still attached to the car and the connector is plugged in, then that's a good way to leave it.
If you remove the EGR valve's internals or disconnect the plug, the car's computer will give you an "Engine Fault" message, since it thinks it can't operate the valve properly.
You can re-program the ECU to not worry about a missing EGR signal but the easiest thing is just leave everything alone but fit the blanking plates to keep gas out of the EGR.
Fit a plate at one of the pipe joints going in to the EGR valve, either by the turbo or at the top, next to the valve. The best position is down by the turbo, so that you don't get gas/soot travelling in to the pipe and clogging it up.
It doesn't do any harm if it clogs up but you would need to unclog it if you wanted to un-blank the EGR any time in the future. However, the nuts at the connection down by the turbo are usually seized and rusty and could snap off... so it's easiest to fit the plate at the top.
Also fit another plate between the EGR and the inlet manifold. Otherwise you can get inlet charge (air/diesel and any oil that gets blown into the manifold from the crankcase breather) settling inside the EGR and potentially clogging it. If it gets clogged and can't move, you'll get an "Engine Fault" message on the dash. It's best if the EGR is cleaned, and then isolated with a plate at both ends.
There's no mechanical problem with a blanked off EGR valve otherwise.
The EGR works by opening up, to let some exhaust gas get sucked back up to the inlet manifold. That exhaust gas contains carbon dioxide, soot, carbon monoxide and nitrous oxides, which by passing through the combustion chamber a second time, are burnt/further oxidised so the exhaust gas (once it escapes out of the back) contains marginally more CO2 but less NOx and soot.
By blanking the valve, the exhaust gas comes out containing more NOx and soot..but marginally less CO2, so Greta will be happy at least.
The car adjusts the inlet mixture by measuring how much oxygen is in the exhaust gas.
The engine reduces the amount of fuel it injects until the exhaust gas is within tolerance.
By blanking the EGR, some of the "air" in the cylinder that used to be recycled exhaust gas, is now clean air (which contains oxygen), so the engine can burn more charge, so injects more fuel and makes more power... obviously at the expense of NOx and soot.
If your turbo was clogged, I would look at a few things.
a) Is the oil level anywhere near "MAX"? If so, then the beast will be blowing oil out of the breather and into the inlet manifold. If you remove the plastic pipe from the metal manifold and have a look in there, it should be dry (let's say "moist") but you will probably have a small puddle of engine oil.
Run the oil level at around 75-80% full. The startup check will show you the level so you can't get very low on oil unless you're not paying attention. If the last "lemon" on the gauge is empty but the others are filled in black, then that's good.
b) Does the car do a lot of short trips? If so, then your mum doesn't need a 1.9ltr diesel. It needs a good run occasionally, to get properly warmed up and burn out the soot/sludge around the turbo.
c) Does the car do low mileage and gets an oil change every 12,000 miles? If so, the oil can be dirty/black from not much use, which is more likely to turn to sludge and block oilways. Change the oil/filter every 12 months, if the mileage is less than 12k a year.
Ralf S.