Approach

Get to the Couvercle hut for example by the summer route from Montenvers.:
From the Aiguille du Midi by the classic Vallée Blanche or more interestingly by the Envers du Plan.
If coming by the Envers du Plan at Point 3626m  (IGN), go to the SE on a slope of S4 for 50m, bergschrund at its base. Then link steep and flattish section in a zone of crevasses direction E to reach a large flattish area at 3150m.  From here traverse to the E to gain the slope at S3/S4 which descends to the Requin hut. Pass to the S of the hut to reach the "Salle à Manger" and the Tacul glacier. Continue by the true right bank of the glacier, if feasible, to the junction with the Leschaux glacier at about 2100m.  Cross this glacier to reach the foot of the 4 ladders and some ramps before an easier path leads up to the Couvercle hut, (2586m).

Ascent Pointe Isabella

After a short descent onto the Talèfre plateau, go W towards the Col des Courtes. At 3300m there is a flattish area under the seracs of the Courtes glacier.
Option 1  If there is not a bergshrund, go up the centre of the glacier.
Option 2  If a bergshrund blocks this way, go along the true right side of the Courtes glacier, keeping as close to the rocks as feasible.  (Careful danger from collapsing seracs.) At a very steep ice wall take an easy,  rocky ledge to the left to reach a flattish area.  2 protection pegs in situ and an abseil point, (slings) for the descent.  (Very exposed to seracs.)


You now have to make the choice between going between the seracs in the centre of the glacier and the W shoulder. Then climb a short N facing slope until a little ridge leads to a mixed section (PD  alpine grade) This leads to the ridge and to the Trient plateau.  From here the summit is gained by short, easy rock climb.

Descent

Follow the ascent route, but before the mixed section al the level of a little col in the ridge, go down a steep gully, (more than 40º for 100m) with a very narrow section (3m) between ice and rocks. Can be seen during the ascent. At the foot of the gully a little bergschrund should be passed without difficulty on the right.  (Seracs, do not dawdle).  Rejoin the ascent route and follow it past the Couvercle hut and go to Montenvers train by the Mer de Glace.